Solid ink or phase change ink printers conventionally receive ink in a solid form, either as pellets or as ink sticks. The solid ink pellets or ink sticks are typically inserted through an insertion opening of an ink loader for the printer, and the ink sticks are pushed or slid along the feed channel by a feed mechanism and/or gravity toward a heater plate in the heater assembly. The heater plate melts the solid ink impinging on the plate into a liquid that is delivered to a print head for jetting onto a recording medium.
One problem faced in solid ink technology is differentiation and identification of ink sticks to ensure the correct loading and compatibility of an ink stick with the imaging device in which it is used. The wrong color of ink stick in a feed channel, ink sticks intended for different solid ink printers, use of non-qualified ink, etc. may impact image quality or even damage the solid ink imaging device. Provisions have been made to ensure that an ink stick is correctly loaded into the intended feed channel and to ensure that the ink stick is compatible with that printer. For example, the correct loading of ink sticks has been accomplished by incorporating keying, alignment and orientation features into the exterior surface of an ink stick. These features are protuberances or indentations that are located in different positions on an ink stick. Corresponding keys or guide elements on the perimeters of the openings through which the ink sticks are inserted or fed exclude ink sticks which do not have the appropriate perimeter key elements while ensuring that the ink stick is properly aligned and oriented in the feed channel. Another method that has been implemented to aid in the identification of an ink stick by a printer control system is the incorporation of encoding features into the exterior surface of ink sticks that interact with sensors in the ink delivery system. Ink stick data may be encoded into these features by configuring the features to interact with one or more sensors in an ink loader to generate a signal or coded pattern of signals that corresponds to information specific to the ink stick.
Emerging phase change ink jet technologies have reduced the time for generating solid ink images, and, consequently, have a high ink consumption rate. As a consequence, larger capacity solid ink delivery systems are needed. To increase the amount of ink that may be loaded in an ink delivery system, solid ink delivery systems have been provided with non-linear feed channels. Non-linear feed channels may include any number of linear and curved sections that can feed and guide ink sticks from an insertion end the ink delivery system to an ink melting assembly of the ink delivery system. The feed channels are typically at least partially enclosed in order to retain, orient, and guide the ink sticks along the feed path and to prevent ink debris in one channel from contaminating the other channels or the interior of the imaging device.
The increased capacity of solid ink delivery systems having non-linear feed channels has prompted the development and use of ink sticks having a larger length to width aspect ratio. The use of “longer” ink sticks lessens the frequency at which the solid ink in the ink delivery system has to be replenished. Larger ink sticks, however, may have greater fabrication stresses than smaller ink sticks due to the nature of the slow cooling rate of the ink and the difference in post forming shrinkage between the outer and inner ink volumes. Therefore, larger ink sticks may be more prone to breaking into multiple smaller pieces when mishandled. Broken ink sticks may not feed reliably resulting in undesirable skewing and jamming of the ink stick pieces in the feed channels.
In addition, increasing the size of the ink sticks may result in a corresponding increase in the tolerances for construction of the corresponding ink delivery system. These increased tolerances may lead to larger clearances around the keying, guiding, alignment, and/or orientation features as well as sensors in the solid ink delivery system. These enlarged clearances may allow undesirable skewing and jamming of the ink sticks in some ink feed channels as well as incorrect positioning of ink stick encoding features with respect to the corresponding sensors. Moreover, the increased clearances may allow the uncontrolled passage of smaller ink sticks and/or pieces of broken ink sticks to the melt assembly of the ink delivery system. If the smaller ink sticks or ink stick pieces are incompatible with the phase change ink jet printer in which they are being used, considerable errors and malfunctions may result.